The clarification of industrial effluent is normally effected by alternatively agitating and letting the effluent settle, and lifting floating scum from the surface of the effluent or scraping sediments at the bottom of the reservoir. The clarification process is often accompanied by a fermenting action and a generation of odorous bio-gases, and/or the release of volatile organic carbons. For environmental reasons, these gases must be collected and treated. Therefore, a clarification reservoir, or clarifier, is preferably covered and sealed to contain the off-gases. Also, a clarifier preferably has a piping system to transport the off-gases to a gas treatment plant.
An industrial clarifier is often circular in shape. The reservoir typically has a central column supporting a motor, a gearbox, and a bearing assembly carrying a surface-skimming boom, a bottom rake or both. These equipment must be accessible for inspection, repair or preventive maintenance. Therefore a first preferred feature of a clarifier cover consists in its ability to be opened, to inspect, repair or maintain the boom, the rake, the circumferential launder or other equipment inside the reservoir. A second preferred feature is that the cover must be adaptable to the integration of a catwalk to the central column, to allow access to the machinery on the central column at all times.
The covering of a clarifier is often associated with the implementation of environmental regulations. Therefore a cover is often installed on an existing clarifier which was not designed to support a cover structure. Therefore, the retrofit installation of a cover over an existing clarifier must be done in such a way that the cover does not apply a substantial load or side stress on the central column inside the clarifier.
Another preferred feature in a clarifier cover is that the enclosed volume above the level of the clarifier must be kept as small as possible to maintain the ventilation of the clarifier as efficient and as economically as possible.
Examples of various systems available for covering a reservoir are described in the following documents:
U.S. Pat. No. 3,130,488 issued on Apr. 28, 1964 to G. Lindstrom; PA0 U.S. Pat. No. 3,683,427 issued on Aug. 15, 1972 to H. C. Burkholz et al.; PA0 U.S. Pat. No. 4,136,408 issued on Jan. 30, 1979 to E. L. Dahlbeck et al.; PA0 U.S. Pat. No. 4,400,927 issued on Aug. 30, 1983 to A. M. Wolde-Tinase; PA0 U.S. Pat. No. 4,951,327 issued on Aug. 28, 1990 to V. J. Del Gorio, Sr.; PA0 U.S. Pat. No. 5,381,634 issued on Jan. 17, 1995 to S. Pietrogrande et al; PA0 U.S. Pat. No. 5,943,709 issued on Aug. 31, 1999 to H. Y. Chiu;
Although the cover structures of the prior art deserve undeniable merits, it is believed that a need still exists in the industry for a clarifier cover which has a low profile, which does not apply substantial load on the central column of a clarifier, which is easily openable for inspection, repair or maintenance of the equipment inside the clarifier and which is strong and durable and can accommodate a catwalk to the central column.